Adding Macrons using emacs:

https://www.stat.auckland.ac.nz/~paul/Reports/maori/maori.html
 The macron is the only accent required for written Māori and the accent can only be applied to vowels, so the full set of accented characters are:
lower case a, with macron 	ā 		upper case A, with macron 	Ā
lower case e, with macron 	ē 		upper case E, with macron 	Ē
lower case i, with macron 	ī 		upper case I, with macron 	Ī
lower case o, with macron 	ō 		upper case O, with macron 	Ō
lower case u, with macron 	ū 		upper case U, with macron 	Ū 

http://emacs.1067599.n8.nabble.com/Entering-vowels-with-macrons-td72136.html
	Ctrl+\
	type rfc1345 (and enter)
	type &a- to get a-macron
	Then Ctrl+\ to toggle back to default input
	(Can thereafter toggle with Ctrl+\ to get back to rfc1345 input method)


OTHER:
https://sachachua.com/blog/2011/04/writing-macrons-linux-latin-pronunciation/
To add macrons: Ctrl-\ "latin-alt-postfix". But doesn't have all macronised vowels as used in Te Reo.
Then Ctrl-\ to get default input editor back.
https://www.gnu.org/software/emacs/manual/html_node/emacs/Select-Input-Method.html